Volume control



Get. 30 1934. s z1 1,978,514

VOLUME CONTROL Filed May 22, .1928

Patented Oct. 30, 1934 VOLUME ooNTRoL Sarkes Tarzian, Philadelphia, Pa., assignor to Arthur Atwater Kent Application May 22, 1928', Serial No. 279,691 Renewed April 15, 1932 12 Claims.

My invention relates to control of-volume or amplitude of signals, music or speech as reproduced by radio receiving apparatus, utilizing thermionic tubes, andespecially by suchas involves' high degrees of amplification, and more particularly for which an alternating current source of power supplies current to the thermalonic tubes. r

y In accordance with my invention, to effect control of the output energy of a radio frequency amplifier utilizingcascaded circuits, preferably tuned or tunable, coupled by thermionic amplifier tu es, or more specifically to control the volume of reproduced signals, the amplifying property of I at least one of the tubes is substantially eliminated, as by breaking or rupturingthe anode circuit thereof, and signal energy impressed upon the input of the tube is transferred, as by capacity and particularly inherent capacity, to the circuit of the cascade associated with the anode circuit of said one of the tubes. Further in accordance with my invention, and additionally, to effect fine or nice control, the magnitude of energy delivered to or from the amplifier is varied; more particularly, a variable shunting effect is produced upon an input circuit, preferably untunable in character and, of

the first amplifier tube, and still more particu-' larly, the interrupted anode circuit is that of a tube having tuned input and output circuits.

Myinventio-n further resides in the system and method hereinafter described and claimed. I

- For an understanding of some of the various forms my invention may take, reference is to be had to the accompanying, drawing in which:

Fig. 1 is a schematic diagram of a receiving system embodying my invention.

Fig. 2 is a similar diagram of a modification of myginvention.

Fig. 3 is a fragmentary diagram of another modification.

Referring to Fig. 1, the received electro-radiant energy is absorbed by the antenna A or any other equivalent absorption structure. In the quency amplifier tube utilized as a coupling tube in the first-stage of a cascade of radio frequency amplifying, detecting and audio frequency amplifying tubes. Its grid 9 is connected to the antenna A while its cathode or filament f is connected to earth or countercapacity E through the condensers 7c, is which exhibit low reactance at the radio frequencies involved. Connected between grid 9 and'earth or countercapacity E is example illustrated V is a thermionic radio frethe radio frequency choke coil L which substantially completely prevents passage of radio frequency current .therethrough, but serves as a bypass for low or audio frequency disturbances to prevent any substantial effect thereof upon the grid 9.

In the circuit of the anode or plate a of the tube V is the primary of a radio frequency transformer preferably having high step-up ratio and whose secondary is shunted by the variable tuning condenser C one of whose terminals is connected to earth E and the other through the stabilizing resistance 1', generally of several hundred ohms, to the grid 9 of the radio frequency amplifier tube V1. In the anode circuit of the latter is the primary of a second radio frequency step-up transformer T1 whose secondary is shunted by the variable tuning condenser C1 one of whose terminals is grounded at E and the other of which connects through a stabilizing resistance T1 with the grid gof the radio frequency amplifier tube V2 in whose anode circuit is the primary, of a step-up radio frequency transformer T2 whose secondary is shunted by the variable tuning condenser C2 one of whose terminals is connected to E and the other connects through the small grid condenser k1 to the. grid g of the detector tube V3 having the equipotential cathode f1 brought to incandescence by the heater h traversed by alternating current. Between the grid g and cathode fl is connected the grid leak resistance T2 of high magnitude. Between the cathode f1 and the anode a is connected the condenser R2, and in theanode circuit is the primary of the audio frequency transformer T3 whose secondary is in the input circuit of the audio frequency amplifier tube V4 whose anode circuit is coupled by the audio frequency transformer T4 with the input circuit of the audio frequency amplifier tube V5 in whose anode circuit are connected the condenser k3 andthe reproducing or signal translating instrument, such as a loud speaker S.

' G represents generically any source of alternating current, such for example one delivering current at a frequency of 60 cycles per second. Through a lamp socket or other equivalent switching or connecting means 5 the primary of the transformer T5 is'connected with the source G. The transformer T5 has several secondary windings of which 1 supplies so-called raw alternating current to the filaments of the tubes,

V, V1, V2 and V4; 2 supplies alternating current to the heater h of the detector tube V3; and 4 supplies alternating current to the filament of the power amplifying tube V5. The secondary llfl 5 delivers alternating current to the filament of the double-wave rectifying tube 6 whose anodes are connected to opposite ends of the secondary '7. With these transformer secondaries are associated resistances, condensers, and choke coils, constituting an alternating current power unit for supplying current for heating the cathodes of the several tubes, and for supplying filtered rectified alternating current at various suitable voltages for the anode circuits of the tubes.

A system of the character above described is a typical tuned radio frequency amplifier receiver utilizing alternating current or socket power.

The input system of the first tube V1 comprising the antenna and earth connections and the choke coil L, which latter may be omitted if suitable or desirable, is of substantially constant inductance and capacity with the result that there is no reactive effect, due to the intervention of the tube V, upon the first tuned circuit comprising the condenser C. It is therefore practicable to mechanically couple the rotors of the several tuning condensers C, Cl and C2 for single dial tuning or uni-control.

The volume control resistance R is connected at its one terminal 17 with earth E or cathode f of the tube V. Movable along the resistance is the control contact K connected to the grid g of the tube V. By moving the contact K along the resistance R there is produced a variable shunting effect upon the input system or circuit of the tube V, decreasing the signal potential of grid g as the contact K is moved towards the terminal 17. Accordingly the signal effect impressed upon the tube V is varied, with resultant control of the volume of the sounds emitted by the radio speaker S.

The control thus far described has the disadvantage that when the effective value of resistance R is small, that is with few number of turns in circuit between adjustable contact, to reduce the volume of strong or local signals, there are produced foreign, disagreeable noises probably due to the shot effect. Additionally, but a small portion of the resistance is effective, all practical control being secured by adjustment of contact K within a narrow range near terminal 17. To provide a volume control, particularly one suited for use with apparatus utilizing tubes having one or more electrode circuits energized from an ultimate source of alternating current, that is by either rectified and filtered or by raw alternating current, which does not produce extraneous noises and which has a wide effective range for controlling input energies of greatly differing magnitudes, in addition to resistance R there is employed a switch 2', or equivalent, to reduce the total amplification by rendering one of the tubes inoperative as an amplifier. Preferably, the switch controls the anode circuit of a radio frequency tube following the coupling tube V, or in any event, of a tube having tuned input and output circuits.

With the switch 1' in its closed circuit position, the resistance R is adjusted in the usual manner to control volume of signals of low and medium intensity or amplitude as reproduced by loud speaker S. In the event that it is desired to moderate the intensity of loud signals, as of local stations, the switch 1 is moved to its open circuit position, and the resistance R adjusted to effect desired strength of reproduction. Although the tube V1. with its anode circuit deenergized by opening of switch 2', is ineffective as an amplifier, signal energy is transferred to the grid circuit of the following tube V2 through the inherent capacity IC and through the grid to plate capacity Ce. The signal energies through Cc and IC are in opposing relation. The input circuit of tube V1 is under these conditions capacitively coupled to the input circuit of the amplifier tube V2 and in effect the amplifier is converted from a three stage amplifier to a two stage amplifier with two tuned circuits capacitively coupled between two operative amplifying tubes. The number of tuned circuits through which energy transfer is effected remains the same. As the total amplification is decreased and the input voltage permitted to remain reasonably high, the reproduction of local signals is not marred by tube noises and in addition adjustment of contact 70 results in less change of volume per unit of movement with finer gradation.of intensity. The decrease in signal strength effected by opening of switch 2' is greater than the amplifying power of the tube as there is loss of energy in the transfer between the two capacitively coupled tuned circuits.

In the circuit arrangement shown, the windings of the radio frequency transformers, as T1 and'T2, are reversely poled in the sense that the anode connected to the transformer primary is opposite in polarity, insofar as alternating signal energy is concerned, to the grid connected to the transformer secondary. The reverse poling may be procured, for example, by winding the primary and secondary in the same direction, as viewed from the same end, and then reversing the external connections or either the primary or the secondary. The reversal through capacity, as inherent capacity 10, between the input elements of the adjacent stages is effective to oppose tendency of the amplifier to oscillate because of inter-electrode coupling. In the system described substantially complete stabilization is effected by the co-operation of the reversed poling and the resistances r and T1.

The relative magnitudes of the condenser FC connected in shunt to switch 2' and of the gridplate capacity Ce with which it forms a series circuit determine the degree of balance or unbalance of the tuned coupling circuit when switch 1' is open and therefore the amount of energy transferred to the input circuit of tube V2. When condenser F0 is of zero or negligible capacity, the circuit, when switch 2 is open, is substantially completely unbalanced and a maximum of energy is transferred; on the contrary, when the condenser F0 is of large capacity for radio frequencies, the circuit remains balanced, with a minimum transfer of signal. An intermediate value of F0 is chosen to permit of suitably loud volume during reception of fairly strong signals, for example, in the arrangement described the capacity is about 10 to 30 micromicro-farads and exists between parts of the switch, twisted leads thereto, etc. An ordinary small, fixed or variable physical condenser may be used.

The adjustment of resistance R with switch 2' in either of its open or closed positions, or manipulation of switch i to effect control of and change in the range of control of volume does not when alternating current is used to supply current to electrode circuits of the tubes, produce any effect which results in the production of an undesirable hum at low frequency.

The switch i, in a series-feed circuit, as shown, or in a' shunt-feed circuit as in Fig. 3 in which the direct current fiowto the plate through a radio frequency choke in parallel to thetransformer primary, is preferably located in the direct current path, To interrupt the radiofrequencypath of a shunt-feed circuit .wouldproduce degeneration andadversely affect the preceding tuned circuit, that isthe tuned input circuit of the same tube. .r i 1 It will be understood that additional switches may be similarly disposed in association with other tubes, but ordinarily the system as described permits adequate control of the strongest signals as received by apparatus ingeneral use. Furthermore, as above mentioned, the switch '1 may be in the anode circuit of any of the radio frequency amplifier tubes but preferably it is disposed as indicated. i

The input of the tube V may be "tuned as shown in Fig. 2, by a condenser C6 and the coil L may be replaced by a transformer T6, as of the two-coil type and having a step-up ratio, across whose secondary may be connected condenser C6. The adjustable resistance Rl maybe connectedto the terminals of the primary of transformer T2 and the movable contact Kl connected to conductor 18 leading from the positive terminal of the source ofthe anode current supply. Different ranges of volume control may be obtained by connecting themovable member of switch ii to either of two contacts from opposite ends of the primary of transformer T,or by moving it from such engagement. The secondary of transformer T2 maybe included in the input circuit of a detector tube'orofan addi-- tional radio-frequency amplifier tube V6 which may precede a detector. r

The primary and secondary windings of the. radio-frequency transformers need not be re-: versed particularly if other measures are adopted to effect or contribute to stabilization of the amplifier, for example, if stabilizing resistances 1, r1, etc. are of suitably high magnitude.

Insofar as certain aspectsof my invention are concerned, the resistance R, or its equivalent may be omitted although 'in radio receiving apparatus, as described, its inclusion is highly desirable as it effects fine or graduated control of volume whereas switch i controls the volume by a large step.

What I claim is:-

1. In a radio receiving system characterized by the production of noise as an incident to high radio-frequency thermionic tube amplification, the method of reducing the volume of strong signals without substantial adverse effect upon the signal-noise ratio, which comprises changing the direct current difference of potential between the cathode and an electrode of a radiofrequency amplifier tube, while said cathode continues at elevated temperature suitable for electron emission, in such sense and to such extent that the anode current is reduced to a magnitude substantially eliminating amplification of signal and noise currents, transferring signalrepresenting energy beyond said tube, and translating the energy so transferred into observable signals.

2. In a radio receiving system characterized by the production of noise as an incident to high radio-frequency thermionic tube amplification and effecting radio-frequency selectivity by' cascaded tuned circuits, the method of reducing the volume of strong signals without substantial adverse effect upon the signal-noise ratio, which comprises changing the direct current difference of pot'ential between the cathode and an electrode of a radio-frequency amplifier tube, while said cathode continues at elevated temperature suitable for electron emission, in such sense and to such extent that the anode current is reduced to a magnitude substantially eliminating amplification of signal and noise currents, without reducing the number of tuned circuits in cascade transferring signal-representing energy beyond said tube, and translating the energy so transferred into observable signals.

3. In a radio receiving system characterized by the production of noise as an incident to high radiofrequency' thermionic tube amplification, the method of reducing the volume of strong signals without substantial adverse effect upon the signal-noiseratio, which comprises changing the direct current difference of potential between the cathode and an electrode of a radiofrequency amplifier tube in such sense and to such extent that the anode current is reduced to a magnitude substantially eliminating amplification of signal and noise currents, transferring signal-representing energy beyond said tube, independently varying the magnitude of the signal-representing energy, and translating the siglnal-representing energy into observable signa s.

4. In a radio receiving system characterized by the production of noise as an incident to high radio-frequency thermionic tube amplification, the method of reducing the volume of strong signals without substantial adverse effectupon the signal-noise ratio, which comprises changing the direct current difference of potential between the cathode and an electrode of a radio-frequency amplifier tube in such sense and to such extent that the anode current is reduced to a magnitude substantially eliminating amplification of signal and noise currents, simultaneously bringinginto the system an impedance cooperating in the transfer of signal representing energy to a point beyond said tube, and translating the siglnal representing energy into observable signa s.

' 5. A radio receiving system comprising a radio-frequency amplifier effecting high amplification of signal-representing energy and including a radio-frequency thermionic amplifier tube, a volume control comprising means for changing, independently of variation of cathode temperature, the direct current potential of an electrode of said tube with respect to the cathode thereof in such sense and to such extent as substantially to eliminate amplification by said tube, means for transferring signal-representing energy to a point in said system beyond said tube, and means for translating the signal-representing energy so transferred into observable signals.

6. A radio receiving system comprising a radio-frequency amplifier effecting high amplification of signal-representing energy and including a radio-frequency thermionic amplifier tube, a

volume control comprising means for changing the direct current potential of an electrode of said tube with respect to the cathode thereof in such sense and to such extent as substantially to eliminate amplification by said tube, means A for transferring signal-representing energy to a point in said system beyond said tube, a second volume control comprising means for gradually varying the magnitude of the signal-representing energy, and means for translating the Y signal representing energy so transferred into observable signals.

7. A radio receiving system comprising a radio-frequency amplifier effecting high amplification of signal-representing energy and including a radio-frequency thermionic amplifier tube, a volume control comprising means for changing the direct current potential of an electrode of said tube with respect to the cathode thereof in such sense and to such extent as substantially to eliminate amplification by said tube, and means for effecting transfer of signal-representing energy to a point in said system beyond said tube comprising an impedance included, when amplification by said tube has been substantially eliminated, in the normal coupling system, and means for translating the signal-representing energy so transferred into observable signals.

8. A radio receiving system comprising a radio-frequency amplifier efiecting high amplification of signal-representing energy and including a radio-frequency amplifier tube, a volume control comprising means for changing, independently of variation of cathode temperature, the direct current potential of an electrode of said tube with respect to the cathode thereof in such sense and to such extent as substantially to eliminate amplification by said tube, a plurality of tuned circuits independent in number of said volume control means for effecting successive selection of radio-frequency signal-representing energy, means for transferring radiofrequency signal-representing energy to a point in said system beyond said tube, and means for translating the signal-representing energy into observable signals.

9. A radio receiving system comprising a radio-frequency amplifier effecting high amplification of signal-representing energy and in cluding a radio-frequency amplifier tube, a volume reducing control comprising switching mechanism in the output circuit of said tube, a capacity effectively included in circuit when said switching mechanism is in volume reducing position to effect transfer of signal representing energy to a point in said system beyond said tube, means independently operable for effecting nice control of volume, and means for translating the transferred energy into observable signals.

10. A radio receiving system comprising a plurality of cascaded tunable circuits, a radio frequency amplifier tube interposed between said circuits, means for effecting nice control of amplitude of reproduction, and means for simultaneously decreasing the amplification of said tube, While permitting transfer of energy from one of said tunable circuits in advance of said tube to a tunable circuit succeeding said tube, and varying the reactance of the anode circuit of said tube external thereto, thereby increasing for strong signals the effective range of said first named control means.

11. A radio receiving system comprising a plurality of vacuum tubes in cascade, at least one of them being a radio frequency amplifier, a plurality of cascaded tunable circuits at least one of which is interposed between neighboring of said tubes, a source of alternating current, means in parallel receiving current from said source for effecting temperatures of the cathodes of said tubes suitable for electron emission, means for effecting nice control of amplitude of reproduction, and means for simultaneously decreasing the amplification of said tube, while permitting transfer of energy from one of said tunable circuits in advance of said tube to a tunable circuit succeeding said tube, and varying the reactance of the anode circuit of said tube external thereto, thereby increasing for strong signals the effective range of said first named control means.

12. A radio receiving system comprising an absorption structure and a radio-frequency amplifier including an amplifier tube, and volume control means comprising a variable impedance included in said system between said absorption structure and said amplifier to vary the signal transfer to said tube without change of amplification, and means for varying the direct-current potential of an electrode of said tube with respect to its heated cathode to effect substantial change in the amplification of the signal by said tube.

SARKES TARZIAN. 

